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Message-ID: <8a04332e-e7b1-8bc3-d569-5052427bcb13@samsung.com>
Date:   Tue, 12 Jul 2022 14:34:55 +0200
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Subject: Re: [PATCH v4] amba: Remove deferred device addition
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From:   Marek Szyprowski <m.szyprowski@samsung.com>
To:     Saravana Kannan <saravanak@google.com>,
        Russell King <linux@armlinux.org.uk>,
        Philipp Zabel <p.zabel@pengutronix.de>
Cc:     Rob Herring <robh@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        John Stultz <john.stultz@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        kernel-team@android.com, linux-kernel@vger.kernel.org
In-Reply-To: <7482d3af-4b02-4c1d-0386-b0a4ddf529da@samsung.com>
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References: <CGME20220705083944eucas1p23419f52b9529c79c03c8cc23e2aaf4c5@eucas1p2.samsung.com>
        <20220705083934.3974140-1-saravanak@google.com>
        <7482d3af-4b02-4c1d-0386-b0a4ddf529da@samsung.com>
Precedence: bulk

Hi Saravana,

On 12.07.2022 14:25, Marek Szyprowski wrote:
> Hi Saravana,
>
> On 05.07.2022 10:39, Saravana Kannan wrote:
>> The uevents generated for an amba device need PID and CID information
>> that's available only when the amba device is powered on, clocked and
>> out of reset. So, if those resources aren't available, the information
>> can't be read to generate the uevents. To workaround this requirement,
>> if the resources weren't available, the device addition was deferred and
>> retried periodically.
>>
>> However, this deferred addition retry isn't based on resources becoming
>> available. Instead, it's retried every 5 seconds and causes arbitrary
>> probe delays for amba devices and their consumers.
>>
>> Also, maintaining a separate deferred-probe like mechanism is
>> maintenance headache.
>>
>> With this commit, instead of deferring the device addition, we simply
>> defer the generation of uevents for the device and probing of the device
>> (because drivers needs PID and CID to match) until the PID and CID
>> information can be read. This allows us to delete all the amba specific
>> deferring code and also avoid the arbitrary probing delays.
>>
>> Cc: Rob Herring <robh@kernel.org>
>> Cc: Ulf Hansson <ulf.hansson@linaro.org>
>> Cc: John Stultz <john.stultz@linaro.org>
>> Cc: Saravana Kannan <saravanak@google.com>
>> Cc: Linus Walleij <linus.walleij@linaro.org>
>> Cc: Sudeep Holla <sudeep.holla@arm.com>
>> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
>> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
>> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
>> Cc: Russell King <linux@armlinux.org.uk>
>> Signed-off-by: Saravana Kannan <saravanak@google.com>
>> ---
>>
>> v1 -> v2:
>> - Dropped RFC tag
>> - Complete rewrite to not use stub devices.
>>
>> v2 -> v3:
>> - Flipped the if() condition for hard-coded periphids.
>> - Added a stub driver to handle the case where all amba drivers are
>>    modules loaded by uevents.
>> - Cc Marek after I realized I forgot to add him.
>>
>> v3 -> v4:
>> - Finally figured out and fixed the issue reported by Kefeng (bus match
>>    can't return an error other than -EPROBE_DEFER).
>> - I tested the patch on "V2P-CA15" on qemu
>> - Marek tested v3, but that was so long ago and the rebase wasn't clean,
>>    so I didn't include the tested-by.
>>
>> Marek/Kefeng,
>>
>> Mind giving a Tested-by?
>
>
> Yes, it looks that it still works fine.
>
> I've tested it by changing the Exynos power domain driver to 
> initialize from late_initcall. This in turn lead me to a bug in 
> generic pm_domains code in __genpd_dev_pm_attach(), which returns -2 
> if the pm domain driver is not yet registered. After fixing that, I've 
> successfully observed the deferred probe of PL330 driver on Exynos 
> 4210 based boards both with this patch and without (with the old timer 
> based code).


While preparing a fix for the above issue in genpd I found that it has 
been introduced by your commit 5a46079a9645 ("PM: domains: Delete usage 
of driver_deferred_probe_check_state()"). I didn't analyze it enough, 
but it looks that something is missing there if we are trying to probe 
amba device. I assume that returning -EPROBE_DEFER unconditionally there 
is also not a valid solution?


>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>
>
>> -Saravana
>>
>>   drivers/amba/bus.c | 317 +++++++++++++++++++++------------------------
>>   1 file changed, 145 insertions(+), 172 deletions(-)
>>
>> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
>> index 0e3ed5eb367b..9590c93b2aea 100644
>> --- a/drivers/amba/bus.c
>> +++ b/drivers/amba/bus.c
>> @@ -130,11 +130,100 @@ static struct attribute *amba_dev_attrs[] = {
>>   };
>>   ATTRIBUTE_GROUPS(amba_dev);
>>   +static int amba_read_periphid(struct amba_device *dev)
>> +{
>> +    struct reset_control *rstc;
>> +    u32 size, pid, cid;
>> +    void __iomem *tmp;
>> +    int i, ret;
>> +
>> +    ret = dev_pm_domain_attach(&dev->dev, true);
>> +    if (ret) {
>> +        dev_dbg(&dev->dev, "can't get PM domain: %d\n", ret);
>> +        goto err_out;
>> +    }
>> +
>> +    ret = amba_get_enable_pclk(dev);
>> +    if (ret) {
>> +        dev_dbg(&dev->dev, "can't get pclk: %d\n", ret);
>> +        goto err_pm;
>> +    }
>> +
>> +    /*
>> +     * Find reset control(s) of the amba bus and de-assert them.
>> +     */
>> +    rstc = 
>> of_reset_control_array_get_optional_shared(dev->dev.of_node);
>> +    if (IS_ERR(rstc)) {
>> +        ret = PTR_ERR(rstc);
>> +        if (ret != -EPROBE_DEFER)
>> +            dev_err(&dev->dev, "can't get reset: %d\n", ret);
>> +        goto err_clk;
>> +    }
>> +    reset_control_deassert(rstc);
>> +    reset_control_put(rstc);
>> +
>> +    size = resource_size(&dev->res);
>> +    tmp = ioremap(dev->res.start, size);
>> +    if (!tmp) {
>> +        ret = -ENOMEM;
>> +        goto err_clk;
>> +    }
>> +
>> +    /*
>> +     * Read pid and cid based on size of resource
>> +     * they are located at end of region
>> +     */
>> +    for (pid = 0, i = 0; i < 4; i++)
>> +        pid |= (readl(tmp + size - 0x20 + 4 * i) & 255) << (i * 8);
>> +    for (cid = 0, i = 0; i < 4; i++)
>> +        cid |= (readl(tmp + size - 0x10 + 4 * i) & 255) << (i * 8);
>> +
>> +    if (cid == CORESIGHT_CID) {
>> +        /* set the base to the start of the last 4k block */
>> +        void __iomem *csbase = tmp + size - 4096;
>> +
>> +        dev->uci.devarch = readl(csbase + UCI_REG_DEVARCH_OFFSET);
>> +        dev->uci.devtype = readl(csbase + UCI_REG_DEVTYPE_OFFSET) & 
>> 0xff;
>> +    }
>> +
>> +    if (cid == AMBA_CID || cid == CORESIGHT_CID) {
>> +        dev->periphid = pid;
>> +        dev->cid = cid;
>> +    }
>> +
>> +    if (!dev->periphid)
>> +        ret = -ENODEV;
>> +
>> +    iounmap(tmp);
>> +
>> +err_clk:
>> +    amba_put_disable_pclk(dev);
>> +err_pm:
>> +    dev_pm_domain_detach(&dev->dev, true);
>> +err_out:
>> +    return ret;
>> +}
>> +
>>   static int amba_match(struct device *dev, struct device_driver *drv)
>>   {
>>       struct amba_device *pcdev = to_amba_device(dev);
>>       struct amba_driver *pcdrv = to_amba_driver(drv);
>>   +    if (!pcdev->periphid) {
>> +        int ret = amba_read_periphid(pcdev);
>> +
>> +        /*
>> +         * Returning any error other than -EPROBE_DEFER from bus match
>> +         * can cause driver registration failure. So, if there's a
>> +         * permanent failure in reading pid and cid, simply say that
>> +         * none of the drivers match.
>> +         */
>> +        if (ret)
>> +            return ret == -EPROBE_DEFER ? ret : 0;
>> +        dev_set_uevent_suppress(dev, false);
>> +        kobject_uevent(&dev->kobj, KOBJ_ADD);
>> +    }
>> +
>>       /* When driver_override is set, only bind to the matching 
>> driver */
>>       if (pcdev->driver_override)
>>           return !strcmp(pcdev->driver_override, drv->name);
>> @@ -368,6 +457,42 @@ static int __init amba_init(void)
>>     postcore_initcall(amba_init);
>>   +static int amba_proxy_probe(struct amba_device *adev,
>> +                const struct amba_id *id)
>> +{
>> +    WARN(1, "Stub driver should never match any device.\n");
>> +    return -ENODEV;
>> +}
>> +
>> +static const struct amba_id amba_stub_drv_ids[] = {
>> +    { 0, 0 },
>> +};
>> +
>> +static struct amba_driver amba_proxy_drv = {
>> +    .drv = {
>> +        .name = "amba-proxy",
>> +    },
>> +    .probe = amba_proxy_probe,
>> +    .id_table = amba_stub_drv_ids,
>> +};
>> +
>> +static int __init amba_stub_drv_init(void)
>> +{
>> +    if (!IS_ENABLED(CONFIG_MODULES))
>> +        return 0;
>> +
>> +    /*
>> +     * The amba_match() function will get called only if there is at 
>> least
>> +     * one amba driver registered. If all amba drivers are modules 
>> and are
>> +     * only loaded based on uevents, then we'll hit a chicken-and-egg
>> +     * situation where amba_match() is waiting on drivers and 
>> drivers are
>> +     * waiting on amba_match(). So, register a stub driver to make sure
>> +     * amba_match() is called even if no amba driver has been 
>> registered.
>> +     */
>> +    return amba_driver_register(&amba_proxy_drv);
>> +}
>> +late_initcall_sync(amba_stub_drv_init);
>> +
>>   /**
>>    *    amba_driver_register - register an AMBA device driver
>>    *    @drv: amba device driver structure
>> @@ -410,160 +535,6 @@ static void amba_device_release(struct device 
>> *dev)
>>       kfree(d);
>>   }
>>   -static int amba_read_periphid(struct amba_device *dev)
>> -{
>> -    struct reset_control *rstc;
>> -    u32 size, pid, cid;
>> -    void __iomem *tmp;
>> -    int i, ret;
>> -
>> -    ret = dev_pm_domain_attach(&dev->dev, true);
>> -    if (ret)
>> -        goto err_out;
>> -
>> -    ret = amba_get_enable_pclk(dev);
>> -    if (ret)
>> -        goto err_pm;
>> -
>> -    /*
>> -     * Find reset control(s) of the amba bus and de-assert them.
>> -     */
>> -    rstc = 
>> of_reset_control_array_get_optional_shared(dev->dev.of_node);
>> -    if (IS_ERR(rstc)) {
>> -        ret = PTR_ERR(rstc);
>> -        if (ret != -EPROBE_DEFER)
>> -            dev_err(&dev->dev, "can't get reset: %d\n", ret);
>> -        goto err_clk;
>> -    }
>> -    reset_control_deassert(rstc);
>> -    reset_control_put(rstc);
>> -
>> -    size = resource_size(&dev->res);
>> -    tmp = ioremap(dev->res.start, size);
>> -    if (!tmp) {
>> -        ret = -ENOMEM;
>> -        goto err_clk;
>> -    }
>> -
>> -    /*
>> -     * Read pid and cid based on size of resource
>> -     * they are located at end of region
>> -     */
>> -    for (pid = 0, i = 0; i < 4; i++)
>> -        pid |= (readl(tmp + size - 0x20 + 4 * i) & 255) << (i * 8);
>> -    for (cid = 0, i = 0; i < 4; i++)
>> -        cid |= (readl(tmp + size - 0x10 + 4 * i) & 255) << (i * 8);
>> -
>> -    if (cid == CORESIGHT_CID) {
>> -        /* set the base to the start of the last 4k block */
>> -        void __iomem *csbase = tmp + size - 4096;
>> -
>> -        dev->uci.devarch = readl(csbase + UCI_REG_DEVARCH_OFFSET);
>> -        dev->uci.devtype = readl(csbase + UCI_REG_DEVTYPE_OFFSET) & 
>> 0xff;
>> -    }
>> -
>> -    if (cid == AMBA_CID || cid == CORESIGHT_CID) {
>> -        dev->periphid = pid;
>> -        dev->cid = cid;
>> -    }
>> -
>> -    if (!dev->periphid)
>> -        ret = -ENODEV;
>> -
>> -    iounmap(tmp);
>> -
>> -err_clk:
>> -    amba_put_disable_pclk(dev);
>> -err_pm:
>> -    dev_pm_domain_detach(&dev->dev, true);
>> -err_out:
>> -    return ret;
>> -}
>> -
>> -static int amba_device_try_add(struct amba_device *dev, struct 
>> resource *parent)
>> -{
>> -    int ret;
>> -
>> -    ret = request_resource(parent, &dev->res);
>> -    if (ret)
>> -        goto err_out;
>> -
>> -    /* Hard-coded primecell ID instead of plug-n-play */
>> -    if (dev->periphid != 0)
>> -        goto skip_probe;
>> -
>> -    ret = amba_read_periphid(dev);
>> -    if (ret) {
>> -        if (ret != -EPROBE_DEFER) {
>> -            amba_device_put(dev);
>> -            goto err_out;
>> -        }
>> -        goto err_release;
>> -    }
>> -
>> -skip_probe:
>> -    ret = device_add(&dev->dev);
>> -err_release:
>> -    if (ret)
>> -        release_resource(&dev->res);
>> -err_out:
>> -    return ret;
>> -}
>> -
>> -/*
>> - * Registration of AMBA device require reading its pid and cid 
>> registers.
>> - * To do this, the device must be turned on (if it is a part of 
>> power domain)
>> - * and have clocks enabled. However in some cases those resources 
>> might not be
>> - * yet available. Returning EPROBE_DEFER is not a solution in such 
>> case,
>> - * because callers don't handle this special error code. Instead 
>> such devices
>> - * are added to the special list and their registration is retried from
>> - * periodic worker, until all resources are available and 
>> registration succeeds.
>> - */
>> -struct deferred_device {
>> -    struct amba_device *dev;
>> -    struct resource *parent;
>> -    struct list_head node;
>> -};
>> -
>> -static LIST_HEAD(deferred_devices);
>> -static DEFINE_MUTEX(deferred_devices_lock);
>> -
>> -static void amba_deferred_retry_func(struct work_struct *dummy);
>> -static DECLARE_DELAYED_WORK(deferred_retry_work, 
>> amba_deferred_retry_func);
>> -
>> -#define DEFERRED_DEVICE_TIMEOUT (msecs_to_jiffies(5 * 1000))
>> -
>> -static int amba_deferred_retry(void)
>> -{
>> -    struct deferred_device *ddev, *tmp;
>> -
>> -    mutex_lock(&deferred_devices_lock);
>> -
>> -    list_for_each_entry_safe(ddev, tmp, &deferred_devices, node) {
>> -        int ret = amba_device_try_add(ddev->dev, ddev->parent);
>> -
>> -        if (ret == -EPROBE_DEFER)
>> -            continue;
>> -
>> -        list_del_init(&ddev->node);
>> -        kfree(ddev);
>> -    }
>> -
>> -    mutex_unlock(&deferred_devices_lock);
>> -
>> -    return 0;
>> -}
>> -late_initcall(amba_deferred_retry);
>> -
>> -static void amba_deferred_retry_func(struct work_struct *dummy)
>> -{
>> -    amba_deferred_retry();
>> -
>> -    if (!list_empty(&deferred_devices))
>> -        schedule_delayed_work(&deferred_retry_work,
>> -                      DEFERRED_DEVICE_TIMEOUT);
>> -}
>> -
>>   /**
>>    *    amba_device_add - add a previously allocated AMBA device 
>> structure
>>    *    @dev: AMBA device allocated by amba_device_alloc
>> @@ -575,28 +546,30 @@ static void amba_deferred_retry_func(struct 
>> work_struct *dummy)
>>    */
>>   int amba_device_add(struct amba_device *dev, struct resource *parent)
>>   {
>> -    int ret = amba_device_try_add(dev, parent);
>> -
>> -    if (ret == -EPROBE_DEFER) {
>> -        struct deferred_device *ddev;
>> -
>> -        ddev = kmalloc(sizeof(*ddev), GFP_KERNEL);
>> -        if (!ddev)
>> -            return -ENOMEM;
>> +    int ret;
>>   -        ddev->dev = dev;
>> -        ddev->parent = parent;
>> -        ret = 0;
>> +    ret = request_resource(parent, &dev->res);
>> +    if (ret)
>> +        return ret;
>>   -        mutex_lock(&deferred_devices_lock);
>> +    /* If primecell ID isn't hard-coded, figure it out */
>> +    if (!dev->periphid) {
>> +        /*
>> +         * AMBA device uevents require reading its pid and cid
>> +         * registers.  To do this, the device must be on, clocked and
>> +         * out of reset.  However in some cases those resources might
>> +         * not yet be available.  If that's the case, we suppress the
>> +         * generation of uevents until we can read the pid and cid
>> +         * registers.  See also amba_match().
>> +         */
>> +        if (amba_read_periphid(dev))
>> +            dev_set_uevent_suppress(&dev->dev, true);
>> +    }
>>   -        if (list_empty(&deferred_devices))
>> -            schedule_delayed_work(&deferred_retry_work,
>> -                          DEFERRED_DEVICE_TIMEOUT);
>> -        list_add_tail(&ddev->node, &deferred_devices);
>> +    ret = device_add(&dev->dev);
>> +    if (ret)
>> +        release_resource(&dev->res);
>>   -        mutex_unlock(&deferred_devices_lock);
>> -    }
>>       return ret;
>>   }
>>   EXPORT_SYMBOL_GPL(amba_device_add);
>
> Best regards

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland